1. Field of the Art
The present invention relates to an optical head used for an optical recording apparatus.
2. Related Art Statement
An optical head is known, which emits a light beam toward an optical recording medium, for storing information on the recording medium, or reproducing information stored on the recording medium. For example, an optical head employs an optical system for directing a laser beam from a laser source to a recording track on an optical or magneto-optical recording disk, and/or for receiving and sensing a light beam reflected from the recording track. The optical system includes an object lens for focusing the laser beam on the surface of the recording disk, and a tracking mirror for deflecting the laser beam so as to position the spot of the laser beam at the center of a recording track of the disk.
3. Problem Solved by the Invention
However, there are various factors which cause a variation in the position of a recording disk relative to the focal point of a beam emitted from an optical head. More specifically, the positions of the recording tracks of the disk may be varied in a direction parallel to the optical axis of the optical head and in a direction perpendicular to the optical axis. To compensate for this positional variation, the focal point of the optical system should be adjusted in both directions indicated above. To this end, a known optical head of the type indicated above incorporates a device for moving the object lens along the optical axis, and a device for changing the angular position of the tracking mirror. If a tracking mirror is not employed, the optical head requires a device for moving the object lens in the direction perpendicular to the optical axis. Therefore, the conventional optical head incorporating such driving devices tends to be heavy, large-sized and complicated in structure. Therefore, the conventional optical head is not satisfactory in its access speed. Further, the use of a relatively large number of optical components leads to increased loss of light during propagation through the optical system. Moreover, the optical components must be aligned with each other with high precision, which makes it difficult to assemble the optical head.